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A giant γ-ray flare from the magnetar SGR 1806–20


Two classes of rotating neutron stars—soft γ-ray repeaters (SGRs) and anomalous X-ray pulsars—are magnetars1, whose X-ray emission is powered by a very strong magnetic field (B ≈ 1015 G). SGRs occasionally become ‘active’, producing many short X-ray bursts. Extremely rarely, an SGR emits a giant flare with a total energy about a thousand times higher than in a typical burst2,3,4. Here we report that SGR 1806–20 emitted a giant flare on 27 December 2004. The total (isotropic) flare energy is 2 × 1046 erg, which is about a hundred times higher than the other two previously observed giant flares. The energy release probably occurred during a catastrophic reconfiguration of the neutron star's magnetic field. If the event had occurred at a larger distance, but within 40 megaparsecs, it would have resembled a short, hard γ-ray burst, suggesting that flares from extragalactic SGRs may form a subclass of such bursts.

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Figure 1: The SGR spike and tail light curve from BAT on Swift.
Figure 2: The pulse profile evolution of the magnetar SGR 1806–20 during the giant flare of 27 December 2004.


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We acknowledge support from NASA (P.M.W., E.R.-R., B.M.G.); the German-Israeli Foundation (Y.E.L.); the NWO (R.A.M.J.W.); the DOE (J.G.); and the Israel-US BSF, the Israel Science Foundation, and the Arnow Chair of Theoretical Physics (D.E.).

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Correspondence to D. M. Palmer.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Figures S1-S3

Supplementary Figure S1, spike and tail time history, 64 ms resolution; Supplementary Figure S2, High resolution spike time history, 1 ms resolution; Supplementary Figure S3, SOPA spectrum of the main spike. (PDF 128 kb)

Supplementary Methods

A description of the use of SOPA and ESP to determine spike fluence, the use of BAT to determine tail fluence, and deadtime correction for BAT, and its limitations. (PDF 97 kb)

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Palmer, D., Barthelmy, S., Gehrels, N. et al. A giant γ-ray flare from the magnetar SGR 1806–20. Nature 434, 1107–1109 (2005).

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